Hiya DevForum! So I am planning on building a tropical waterpark, and I was wondering, what would be the best way to build a waterslide? I know there are plenty of models out there, but they all seem to be very rough and you often get stuck on the overlapping sections. I need something smooth and clean, to make it as realistic as possible. Would I use blender or Roblox? How would I form it?
Any help would be appreciated, thanks! 
I would use Blender and make up separate parts of the slide. Using unions absolutely messes up hitboxes, especially if its a tunnel slide. I would make it in blender, and export parts of it separately to keep a consistent hitbox.
In order to make the slides:
Yes definitely use blender!! Meshes are key in this instance, anything else would be too time-consuming and not give you the desired effect.
I would use a Nerbs Cylinder or a Curve object modifier. There are a lot of good YouTube tutorials on how to use these things, and I promise they will be worth your time.
In order to go down the slide:
I have seen people use transparent parts that make your character sit at the top of the slide then ROBLOX gravity does the rest. I do not know if this is the most effective method, sometimes you stop before reaching the bottom.
Good luck mate and I hope you find some success with this!!